1. Field of the Invention
The present invention relates to an image forming apparatus including belt-shaped transfer members, such as an intermediate transfer belt, a transfer belt, and the like.
2. Description of the Related Art
An image forming apparatus which uses belt-shaped transfer members, such as an intermediate transfer belt (for obtaining an image by transferring a toner image formed on a photosensitive member onto the intermediate transfer belt before transferring the toner image onto a transfer material, such as paper or the like, and thereafter transferring the toner image on the intermediate transfer belt onto the transfer material), a transfer-material conveying belt (for conveying the transfer material to a transfer region in order to transfer the toner image formed on the photosensitive member onto the transfer material), and the like, is effective as a color image forming apparatus or a multicolor image forming apparatus for outputting a color image or a formed image reproduced by synthesizing multicolor images, by sequentially transferring and laminating a plurality of component color images included in color image information or multicolor image information, or an image forming apparatus having a color image forming function or a multicolor image forming function. In such an image forming apparatus, a high-grade cleaning property is required for both of the intermediate transfer belt and the transfer-material conveying belt. Hence, the related art will be described illustrating the intermediate transfer belt.
FIG. 1 is a schematic diagram illustrating a color image forming apparatus (a copying machine or a laser-beam printer) which utilizes an electrophotographic process. In FIG. 1, a drum-shaped electrophotographic photosensitive member (hereinafter termed a xe2x80x9cphotosensitive drumxe2x80x9d) 1, serving as an image bearing member, is rotatably driven in the direction of an arrow at a predetermined circumferential speed (process speed). In a charging process, the photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity by a primary charger 2, and is then subjected to exposure 3 by, image exposure means (not shown). Thus, an electrostatic latent image corresponding to a first color component image (for example, a yellow color component image) of a target color image is formed.
Then, the electrostatic latent image is developed to provide a yellow component image, serving as a first color image, by a first developing unit (a yellow color developing unit 4Y in this case). At that time, since second through fourth developing units, i.e., a magenta color developing unit 4M, a cyan color developing unit 4C and a black color developing unit 4K, do not operate on the photosensitive drum 1, the yellow component image, serving as the first color image, is not influenced by the above-described second through fourth developing units.
An intermediate transfer belt 6 is rotatably driven in the direction of an arrow at a surface moving speed which is substantially the same as (or slightly higher than) the circumferential speed of the photosensitive drum 1. The yellow component image, serving as the first color image, formed on the photosensitive drum 1 is sequentially transferred (subjected to primary transfer) onto the outer circumferential surface of the intermediate transfer belt 6 by an electric field formed by a primary transfer bias voltage applied from a bias-voltage power supply 12 to the intermediate transfer belt 6 via a primary transfer roller 8, while passing through a nip portion between the photosensitive drum 1 and the intermediate transfer belt 6. The primary transfer bias voltage is, for example, within a range between +100 V and +2 kV.
The surface of the photosensitive drum 1 after transfer of the yellow toner image, serving as the first color image, while contacting the intermediate transfer belt 6 is cleaned by a cleaning device 5. Similarly, a magenta toner image, serving as a second color image, a cyan toner image, serving as a third color image, and a black toner image, serving as a fourth color image, are sequentially transferred onto the intermediate transfer belt 6 in a superposed state, to form a synthesized color toner image corresponding to the target color image on the intermediate transfer belt 6.
In the above-described primary transfer process of the toner images of the first through third colors from the photosensitive drum 1 onto the intermediate transfer belt 6, a secondary transfer roller 9 and a belt cleaner 7 are separated from the intermediate transfer belt 6. The secondary transfer roller 9 is disposed at a portion below the intermediate transfer belt 6 by being supported so as to be parallel to a secondary-transfer facing roller 16. After forming the synthesized color toner image corresponding to the target color image on the intermediate transfer belt 6, the secondary transfer roller 9 contacts the intermediate transfer belt 6, a transfer material 10 is fed from a feeding roller 18 to a contact portion between the intermediate transfer belt 6 and the secondary transfer roller 9 at a predetermined timing, and a secondary transfer bias voltage is applied from a bias-voltage power supply 17 to the secondary transfer roller 9. The synthesized color toner image transferred onto the intermediate transfer belt 6 is thereby subjected to secondary transfer onto the transfer material 10.
The transfer material 10 onto which the synthesized color toner image has been transferred is guided to a fixing unit 13 to be fixed by being heated. Upon completion of image transfer onto the transfer material 10, the belt cleaner 7 is brought into contact with the intermediate transfer belt 6 in order to clean toner particles remaining on the intermediate transfer belt 6 after image transfer.
In contrast to a conventional color electrophotographic apparatus including an image forming apparatus in which a transfer material is attached or attracted on a transfer drum and an image is transferred from an image bearing member onto the transfer material, for example, a transfer device described in Japanese Patent Application Laid-Open (Kokai) No. 63-301960 (1988), the above-described color electrophotographic apparatus having the image forming apparatus using the intermediate transfer belt has the advantage that, since an image can be transferred from the intermediate transfer belt without requiring any processing or control (for example, grasping on a gripper, attracting, or providing a curvature) for the transfer material, image transfer can be realized irrespective of the width or the length of the transfer material, ranging from thin paper of about 40 g/m2 to thick paper of about 200 g/m2, such as an envelope, a postcard, label paper or the like.
Although in the case shown in FIG. 1, a first-color toner image through a fourth-color toner image are sequentially transferred from one photosensitive member onto an intermediate transfer belt, there are a method for forming toner images of respective color components on a plurality of corresponding photosensitive members and sequentially transferring the toner images onto an intermediate transfer belt, a method for forming toner images of a plurality of color components on one photosensitive member and then simultaneously transferring the toner images onto an intermediate transfer belt, and the like. There are, of course, electrophotographic apparatuses each using an intermediate transfer belt in which a full-color image is output after passing through an image forming process other than the above-described process. Image forming apparatuses, such as color copiers, color printers and the like, each using such a belt-shaped transfer member have started to operate on the market.
However, when repeatedly using an image forming apparatus using a belt-shaped transfer member actually in various environments, the following problems still exist.
For example, the efficiency of transferring toner from an image bearing member, such as a photosensitive drum, onto a transfer member, such as an intermediate transfer member or the like, or onto a transfer material, and the efficiency of transferring toner from a transfer member, such as an intermediate transfer member or the like, onto a transfer material are not yet sufficiently high. Accordingly, it is required to provide a cleaning device for the transfer member. Particularly when a large amount of toner particles remain after image transfer, the lives of members, such as the transfer member and the like, are shortened, and the cleaning device inevitably has a complicated configuration and a high cost, resulting in a high cost of the apparatus.
In order to improve the efficiency of toner transfer, the inventors of the present invention have proposed, as described in Japanese Patent Application Laid-Open (Kokai) No. 8-320591 (1996), to achieve improvement of the transfer efficiency by specifying the shape of toner and the surface characteristics of an intermediate transfer member.
As for a cleaning member for a transfer member, various cleaning methods have been proposed, such as a cleaning method using a brush-shaped cleaning member, a cleaning method using an electric field, and the like. Among these cleaning methods, a blade cleaning method is preferable because the structure of a cleaning device is relatively simple, and reliability is high, and a low cost can be realized.
In the above-described approach described in Japanese Patent Application Laid-Open (Kokai) No. 8-320591 (1996), when using a cleaning blade as a member for cleaning toner particles remaining on an intermediate transfer member after image transfer, a failure in cleaning sometimes occurs. Such a phenomenon is pronounced when using a belt-shaped member as the intermediate transfer member. It is considered that in contrast to a case of using a stiff intermediate transfer member having the shape of a roller or the like, in the case of using a belt-shaped transfer member, uniform contact of a blade is difficult to realize.
In Japanese Patent Application Laid-Open (Kokai) No. 9-258474 (1997), image formation is performed by combining spherical toner with an apparatus including an intermediate transfer belt. However, no consideration has been taken to the physical properties of the intermediate transfer belt.
It is an object of the present invention to provide a full-color image forming apparatus including a belt-shaped transfer member and having a high transfer efficiency and a stable cleaning property.
According to one aspect, the present invention which achieves the above-described object relates to a full-color image forming apparatus for forming an image on a transfer material by transferring a toner image formed on an image bearing member onto a transfer material. The apparatus includes a belt-shaped transfer member for transferring a toner image from the image bearing member onto a transfer material, and a cleaning blade for cleaning the belt-shaped transfer member by being brought into contact therewith. Shape coefficients SF-1 and SF-2 of a toner for forming the toner image have values of 100xe2x89xa6SF-1xe2x89xa6125, and 100xe2x89xa6SF-2xe2x89xa6125, respectively. The belt-shaped transfer member has a seamless shape in which a seam is absent. An amount of abrasion of a surface of the belt-shaped transfer member is equal to or less than 10.0 mg. An angle of contact of the belt-shaped transfer member with respect to water is at least 60xc2x0. A slide resistance of a surface of the belt-shaped transfer member is equal to or less than 1 N.
The foregoing and other objects, advantages and features of the present invention will become more apparent from the following detailed description of the invention taken in conjunction with the accompanying drawings.